One of the excellent features of new Windows devices is that disk encryption is built-in and turned on by default, protecting your data in case your device is lost or stolen. But what is less well-known is that, if you are like most users and login to Windows 10 using your Microsoft account, your computer automatically uploaded a copy of your recovery key – which can be used to unlock your encrypted disk – to Microsoft’s servers, probably without your knowledge and without an option to opt-out.
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As Green puts it, “Your computer is now only as secure as that database of keys held by Microsoft, which means it may be vulnerable to hackers, foreign governments, and people who can extort Microsoft employees.”

Source: Recently Bought a Windows Computer? Microsoft Probably Has Your Encryption Key